Vision
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* Base city vision radius sq 5
* City vision radius increased in size 15 cities
* City vision radius increased when player knows Radar


 Migration
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* People may spontaneously migrate to better city
* Culture affects city migration score slightly


Veteran Levels
==============

* Military units have four veterancy levels
* Workers have three veterancy levels and their speed increases
  as they gain those levels
* Diplomat units have three veterancy levels
* Regular buildings enabling building of veteran units give two veterancy
  levels. Wonders giving such bonuses give just one veteran level.
  Effects from regular buildings and wonders are cumulative.